The present invention relates generally to equipment utilized in subterranean wells and, in an embodiment described herein, more particularly provides an apparatus having a releasable lock incorporated therein.
In many situations encountered while servicing a subterranean well, it may be desirable to delay or prevent actuation of a device until a desired condition is achieved. For example, a ball valve or other type of valve may be positioned in the well for controlling fluid flow through a tubular string in which the ball valve is interconnected. Operation of the ball valve to an open or closed position may not be desired until a predetermined fluid pressure is applied to the tubing string or an annulus between the tubing string and a wellbore of the well, a predetermined differential pressure is applied between the tubing string and the annulus, etc.
In these situations, a releasable lock is sometimes used to prevent operation of the device until the desired condition is achieved. The releasable lock is interconnected between a force generating assembly (a portion of an apparatus which generates a force to operate the device when the desired condition is achieved) and the device. When the desired condition is achieved, the releasable lock transmits the force to the device in such a manner that the device is operated, but otherwise resists such transmission of the force to the device. Thus, the releasable lock is a force transmitting assembly, which selectively permits application of the force to the device to operate the device.
In the past, hydraulic chambers and shear members, such as shear pins, have been used to construct releasable locks. When a hydraulic chamber is used, fluid is displaced from the hydraulic chamber in response to the desired condition being achieved. When shear members are used, the members are made to shear when a predetermined force is applied thereto.
Unfortunately, releasable locks using either of these elements suffer from some drawbacks. Shear members are susceptible to fatigue failure where a force is repeatedly applied to them, such as when pressure fluctuations are experienced while running into the well. Hydraulic chambers require a degree of precision in filling the chambers with appropriate types and volumes of fluid, are time-consuming and maintenance intensive, etc.
Therefore, what is needed is a releasable lock which is convenient in its assembly, use and maintenance, and which permits accurate operation of a device in a well, regardless of pressure fluctuations experienced while running into the well. It is accordingly an object of the present invention to provide such a releasable lock and apparatus incorporating the releasable lock therein.